This invention relates to satellite communications and, more particularly, to an improved transmitter section of a communications satellite.
The current trend in communications satellite design is towards a multibeam antenna (MBA) design on the spacecraft to provide high antenna gain and frequency reuse capability. A problem with the MBA concept for focal point feed parabolic reflector antenna systems is the difficulty of moving power from one beam to another.
For multibeam antenna systems where each beam is formed by a single feed element, a Hybrid Matrix Power Amplifier (HMPA) can be used to allow power to be moved between beams (FIG. 1). However, for such antenna systems, the edge of beam gain is low due to the beam shape and the beam separation is determined by the physical size of the feed elements.
To provide high antenna gain and good beam overlap for a focal point feed parabolic reflector antenna system, beams may be formed from multiple feed elements. An example of such a system is described in copending U.S. patent application Ser. No. 197,328 filed on May 28, 1988 and assigned to the assignee of the present application. The disclosure of U.S. patent application Ser. No. 197,328 is hereby incorporated by reference. The system described in that application combines the capabilities of a low level beam forming network (LLBFN) with the hybrid matrix power amplifier (HMPA). The LLBFN allows efficient beam overlap using multiple element feed clusters where adjacent beams share feed elements. The HMPA allows the power for any feed element or set of feed elements to be distributed evenly among the individual power amplifiers providing flexible assignment of traffic between beams up to the limit of the spacecraft power resources.